1. Field of the Invention
The present invention relates to a cryogenic refrigerator that includes a rotary valve.
2. Description of the Related Art
Gifford-McMahon (GM) refrigerators are known as cryogenic refrigerators that can produce cryogenic temperatures. A GM refrigerator produces a refrigeration effect using the Gifford-McMahon refrigeration cycle, which involves reciprocating a displacer within a cylinder using a drive mechanism to create a volume change in a space within the cylinder.
In the GM refrigerator, high-pressure working gas (e.g., helium gas) is supplied to a cylinder, and the working gas is adiabatically-expanded and cooled to a cryogenic temperature. The working gas that is adiabatically-expanded and cooled to a cryogenic temperature is then warmed by absorbing heat from its surrounding and exchanging heat with a regenerator material. After reaching room temperature, the working gas is discharged from the cylinder. In this way, a cryogenic temperature may be maintained within the cylinder. The working gas discharged from the cylinder is transferred to a compressor and is compressed by the compressor. In this way, the working gas is turned into high-pressure working gas. The high-pressure working gas is then reintroduced into the cylinder of the GM refrigerator.
In order to supply the high-pressure working gas into the cylinder and discharge the working gas that is reduced to a low pressure outside the cylinder, the GM refrigerator uses a valve mechanism that is configured to switch between supplying and discharging the working gas in synch with a reciprocating motion of a displacer that is arranged within the cylinder. For example, the GM refrigerator may use a rotary valve as the valve mechanism.
A rotary valve includes a stator valve and a rotor valve, which is rotated with respect to the stator valve. By rotating the rotor valve, the rotary valve may switch paths connected to the cylinder between a supply side path and a discharge side path of the compressor. Also, in the rotary valve of a GM refrigerator, the rotor valve needs to be pressed toward the stator valve or vice versa in order to prevent the working gas from leaking. In one known GM refrigerator, the pressure of the working gas supplied to the cylinder is used to press the stator valve toward the rotor valve. More specifically, when high-pressure working gas is supplied from a side opposite a sliding face of the stator valve, the pressure of the working gas acts on a face of the stator valve on the opposite side of the sliding face of the stator valve, and this pressure is used to press the stator valve toward the rotor valve.
In another known GM refrigerator, a spring is used as mechanism for pressing the stator valve toward the rotor valve. In such a GM refrigerator, the spring is arranged on a face of the stator valve on the opposite side of the rotor valve, and the spring force of the spring is used to press the stator valve toward the rotor valve.